Production of alternating currents



Feb. 10, 1925. r

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6, 14 and the drop through inductance 17. 'VVith the proper proportion of inductance 17 and the proper grid excitation, the plate Voltage of the valve which is carrying current may be maintained at the desired low rent will produce square blocks of plate cur-' rent at substantially constant plate voltage. Square blocks of grid current can be obtained by the arrangement shown in Fig. 1. Energy is supplied to the grid by the coupling between 6 and 9 and the total grid current is kept more or less constant by an inductance 18'. This grid currentnaturally flows from that grid, which is most positive' at any instant, and since the total is constant each rid receives current in square blocks as required.

If inductances 17 and 18 are not large enough to keep the total current constant in the grid and plate circuits, there will be cyclic ripple variations in the current in each of these circuits, as indicated by curves in Fig. 2. In these curves X represents the impressedJ). C. potential while A represents the potential of the midpoint 7 of 'induc tance 6, which corresponds to the counterelectromotive'force of the oscillating circuit. At points f the counter-electromotive force is zero. There is therefore nothing to prevent a rise in current except the inductance 17. The plate current which is represented by curve B will therefore be rising at these points. To preserve the average the counter-electromotive force at points 9 and h is higher than the impressed potential X. The plate current I) is therefore falling at points 9 and h.

Similarly, curve C represents electrometive force at the midpoint 10 of the winding 9, which is due to the rectifier action of the grids. 'Since this potential is depended upon to make the grid current flow and since this potential is zero at points f, the grid current represented by curve D is falling at these points and rising at points 7 and ii. The amplitude of the variation is dependent upon the value of inductance 18.

An inspection of the curves B and B shows that when the plate current is rising the grid current is falling, and vice versa. lit is therefore evident that with this arrangement the desired proportlonahty be eases? tween grid current and plate current will not he maintained, and as a result of such variation from the normal the losses will be increased. lVith the arrangement thus far described therefore it is evident that it is important to make inductances 17 and 18 large enough to prevent any material variation in either the plate current or the grid current during the cycle.

ll'ith high frequency and high voltage the design of inductances 17 and 18 becomes increasingly difficult. For instance, if the power factor of the circuit 6, 1 1 is 10% the energy current is of the circulating current. The direct current is rough- 1y equal tothis energy current so that if the current ripple in the plate circuit is not to exceed 10% of the direct current, then the .ohmic impedance of inductance 17 must be 100 times that of 6. The lowest frequency impressed upon 17 is twice the fundamental so that in henries the inductance of 17 must be fifty times that of 6. .At radio frequencies and with apparatus of reasonably'sniall size .it is extremely diflicult to design the inductance 17 sothat its natural resonant frequency will be suthciently above the frequency at which it is required to work. The circuit thus far described is therefore practically limited in its utility'to frequencies not above a few hundred cycles.

To overcome the disadvantages above set forth and permit the circuit described to operate successfully at higher frequencies, the inductances 17 and 18' are magnetically coupled. By this means the voltages induced by plate current ripples in 17 may be utilized to cause a grid current ripple similar to that of the plate current. By this means the grid current ripple is shifted 180 to the position shown by the clotted curve E. It will be seen that with a grid current corresponding to curve E the grid current is rising and falling in unison with the plate current, and that the desired proportionality between the two currents may he maintained. It is therefore possible even with a considerable ripple in these currents to conform constantly to the conditions of minimum valve loss.

lnductances 1? and 18 in addition to being magnetically coupled may be connected through a capacity 19 shown in dotted line, or the direct current power supply may act as such a coupling capacity. if there should he no oscillations produced in the circuits 6, 1.4. or 15, it is apparent that inductances 17 18 may function as the grid and plate inductances of an oscillating circuit, the capacity coupling of which is furnished by coils 6 and 9, and by such other parts the main oscillating circuits as are exposed to one another. This circuit m s pport parasitic oscilla tions in which two valves operate in parallel the frequency is the natural preferred embodiment of my invention, it

will be apparent that it is by no means limited to the particular embodiment shown and described, but that many modifications of the particular apparatus employed, as well as the circuit connections used, may be made Without departing from the scope of my invention as set forth in the appended claims.

hat I claim as new and desire to secure by Letters Patent of the United States, 1s, 1

1. The combination in a system for producing alternating current of a pair of electron discharge devices each having an anode, a cathode and a control electrode, an inductive winding having its terminals connected to the anode of said devices and an intermediate point connected to source of 1 direct current through an inductance, a

second inductive winding which is inductive ly related to the first and has its terminals connected to the control electrodes of said ductively related to each other.

2. A system for producing alternating currents comprising a lurality of electrondischarge devices having plate andgrid ci'r? cuits, a source of direct current for supplying current to the plate circuits, means com prising :an inductance for reducing the variations in the current supplied by'said source, means for impressing. an alternating current upon the grid circuits and means comprising:- a second inductance in'the rid circuit magnetically coupled to the whereby such variations as do occur in the supply current are communicated to the current in the grid circuit.-

' A system for v'produc'ing alternating currents comprising a plurality of electron discharge devices having plate and grid circuits. a coupling between said grid and plate circuits for furnishing excitation to thegrids to maintain oscillations. a source.

of direct current for supplying current to the plate circuits, means comprising an inductance for reducing the variations in the current supplied by said source, and means comprisingan inductance in the grid circuit magnetically coupled to the first inductance, whereby such variations of current as may occur in the supply current produce corresponding current variations in the grid circuit.

4. A systen'i for producing alternating currents comprising: a plurality of electron discharge devices having plate and grid circuitspa coupling: between said grid and plate circuits f-or furnishing excitation to the, grids to maintain oscillations, a source of direct current for supplying current to tlievplate circuitsand a second coupling between. the supply circuit and the; grid ciruits for n uuntain'ingrv substantially, constant the proportionality between the currents in the plate and grid circuits.

In witnesswhe-reof, I have hereunto set my hand-this 13th da of December. 1923.

- DXVID GI PRINCE.

rst. 

